It has long been recognized that a controlled pattern of equable distribution and a control of velocity of a gas stream at the locus of introduction thereof into gas treating apparatus can materially contribute to increased efficiency of operation and extended operating life of the gas treating components thereof. One area of preferential concern has been in the industrial gas filtration field, and particularly in the fabric filter dust collector field. One type of such fabric filter dust collector, also called a "baghouse", typically employs a large number of tubular fabric filters suspended from a tube sheet and interposed in the path of a particulate laden gas stream to effect the separation of the particulate matter from the gaseous carrier as the latter traverses the fabric filter media in its passage from the dirty air plenum to the clean air plenum portion of the filter housing. Another type of fabric filter dust collector employs filter media in the form of flat panels rather than tubular filter bags. In both such types of dust collector, a particulate laden gas stream conventionally enters the filter housing either through a breach in a portion of the lower housing wall defining a dust collecting hopper and generally changes direction and flows upwardly toward the filter media or enters the housing through an opening in the upper sidewall portion of the collector housing defining at least a portion of the perimeter of the dirty air plenum. The particulate matter borne by the incoming gas stream normally accumulates on the upstream filter medium surface and, unless removed by dislodgement, results in a progressive increase in pressure drop across the filter media and in a concommitant reduction in the rate of gas flow through the filter media. In order to avoid excessive particulate accumulation on the upstream surface of the filter media, the filter media is periodically cleaned by utilization of various known techniques, such as pulse jet and reverse flow cleaning and bag shaking. The outcome of such cleaning operation is that a large part of the accummulated particulates are induced to drop off the filter media surface and fall downwardly, under the influence of gravity and generally countercurrent to normal gas flow, toward and into a collection hopper.
In most industrial fabric filter installations of the type described above, the particulate bearing gas stream approaches the filter through a delivery or conveying conduit having a crosssectional area sized to effect gas stream displacement at sufficiently high velocities, usually in the order of 3500-4000 feet/min., to assure maintaining the particulate matter in suspended entrained condition therein. Antithetically thereto, it has been recognized that high efficiency -- low loss filter operation and increased operating life of the filter components is dependent, at least in substantial part, by an equable distribution of deposited particulates on all the available filter media surfaces; by minimization, if not avoidance, of turbulence in gas flow within the dirty air plenum; by minimization of particulate re-entrainment during or after filter media cleaning and by minimization of localized wear and abrasion of filter components. As is apparent, the high velocity attended operating parameters of the conduit confined approaching particulate bearing gas stream are basically antithetical to the desired optimum parameters of gas stream displacement within the filter housing and the attempted conversion thereof, normally within localized dimensional restraints, conventionally employs transition ducting and the interposition of turning vanes, baffle plates and related gas flow direction and velocity modifiers to the end of hopefully effecting a more equable distribution of the incoming particulate bearing gas stream relative to the available filter media surface and a marked reduction in its approach velocity in a short length of gas stream travel.
The transition of the shape and velocity of the incoming particulate bearing gas stream to the desirable flow conditions within the fabric filter media housing has been a long standing problem in this art. Many expedients, such as expansion of conduit dimension and the use of baffle plates, turning vanes, flow dividers, perforated plate diffusers, gratings, grids, various types of deflector or distribution plates and the selective location thereof in the path of the incoming gas stream and the like have been suggested to enhance fabric filter performance in the separation and collection of industrial dusts. Illustrative of some of such varied expedients are U.S. Pat. Nos. 4,227,903; 4,544,383; 4,655,804; 4,213,766; 3,926,595; 3,831,350; 3,831,354; 3,739,557; 3,425,189 and 3,155,474. While most of such expedients have resulted in some degree of improved performance, the net results have fallen far short of optimum and the problem of achieving high efficiency and economic operation of industrial fabric filter dust collectors remains a continuing one.